Pitcher model
Utricularia bladder
Utricularia bladder TS
External gland/trichome
Carnivorous Plants
Above: left - a 3D computer model of a generalised pitcher of a pitcher plant (similar to Nepenthes). Right - a
drawing of a
Nepenthes pitcher. The pitchers are modified leaves and are beautiful structures and sometimes quite

Pitcher Plants

Pitcher plants are extraordinary carnivorous plants. They have modified leaves that form special receptacles that
contain fluid. Insects and other small animals (and also plant debris) that fall into the pitcher are broken down and
absorbed. In particular, the nitrogen obtained in this way is a valuable nutrient as nitrogen often limits plant growth
and carnivorous plants often occur where nitrogen is in short supply. The pitchers can be quite large and dead rats
are occasionally found inside the very largest. Some pitchers secrete
enzymes and acid to digest their prey, whilst
others rely on bacterial decomposition or both. The enzymes that may be secreted include proteases (digest
proteins) and carbohydrases (digest carbohydrates like starch). Digestion is typically slow and to stop the animals
escaping various tactics are employed. Downward pointing hairs or spines inside the pitcher, combined with a
slippery, waxy surface make it hard for insects to crawl back out!

Darlingtonia, the California pitcher or cobra plant has particularly fascinating pitchers that look like snakes, with
their forked protruding appendage and curved over hoods. A spiral passage connects the digestion chamber to
the outside world and even if trapped insects can navigate this, the hood has a special trick to deceive them - it
fenestrae or translucent windows which allow light through. The insect makes a line for these windows,
believing them to be exits, flies up, bumps into the hood and falls back down the spiral shoot into the trap! This
compensates for the fact that
Darlingtonia does not secrete digestive enzymes, but relies on the slower process of
bacterial decay.

Chance encounter might not be sufficient and pitchers have ways of luring their prey!
Sarracenia purpurea, a
pitcher from NE America has a green pitcher which is red at the top and has nectaries around the aperture and
releases a violet odour. The colour, promise of food and odour all serve to attract insects. Most of these insects
are actually not flies but largely crawling insects and
Sarracenia has a single ventral ridge the ala ventralis (ventral
wing) which is a causeway along which insects can crawl up the pitcher to the slick, waxy surface of the rim
(peristome) - and down they fall! Rows of downward pointing hairs, the slippery inside surface and the viscosity of
the fluid in the trap all make it hard for the insects to get back out. The nectaries secrete an alkaloid narcotic, in
addition to sugar, to anaesthetise the insect, again making it hard for the animal to avoid slipping in!
has nectaries around the waxy rim and large downward-pointing teeth inside the tube and secretes digestive
Nepenthes is a tree-climbing vine.
Left a bladder of Utricularia. Utricularia is a
freshwater aquatic plant which lacks roots and
floats in the water. It gives off stalk-like stolons
which bear small bladders, which contain fluid
under reduced pressure, each no more than 5
mm long.

These bladders are sophisticated traps, primed
and ready to catch prey, which is typically small
crustaceans, like water fleas and copepods, and
insect larvae. These creatures try to hide
amongst the hairs (trichomes) that project from
the bladder (borne on wings (W) in the example
on the left) but these hairs are primed triggers
and when the prey brushes against them the
trap springs open! Water rushes into the
bladder, sweeping along the prey with it. The
trap then seals shut and enzymes digest the
unfortunate victim! R, rostrum; S, stalk; W, wing.
Below: a longitudinal section through one of the bladders. The trap is primed and a flap-like valve (V)
closes the entrance. This valve is wedged shut. Pulling on the trichomes (T) springs the trap, the
valve opens and water rushes in. Inside the bladder lining possesses small glandular hairs or internal
glands (IG), some of these have four cells at their tips (4 end-branches) and are called
, whilst some have two terminal cells and are called bifid glands. The outside of the bladder
contains equidistantly spaced small spherical or nipple-like glands (external glands). The functioning
of these glands are described below.
Utricularia bladder in section
The bifid glands are generally found immediately
below and inside the trap entrance.

Left: transverse sections of
Utricularia bladders.
Leftmost - when primed the bladders side-walls cave
in (they are concave) as the fluid inside the bladder is
at lower pressure than the water outside. Rightmost -
an activated trap - water has rushed in and stretched
the walls of the bladder which are now convex (curve
The internal glands consist of an elevated basal cell, which is part of the epidermis (cell layer
covering the wall of the bladder). Above this is a pedestal cell and above this are 2 (bifid gland) or
4 (quadrifid gland) capital or terminal cells. Black and dark shading indicate water-impervious
regions of the cuticle and cell walls respectively. These ensure that water can only enter or leave
the gland through the terminal cells (which lack any substantial cuticle) and also block the
apoplastic pathway between the basal and pedestal cells.


These glands pump out water from the inside of the trap when it is being primed, lowering the
pressure in the trap and creating the suction when the trap springs open. This process is rapid
and so probably occurs through the apoplast (cell walls) as shown by the blue arrow. The
movement of this water is actively driven. Pumps in the cell-surface membrane of the pedestal cell
use cellular energy to pump water from the apoplast across the membrane into the cytoplasm of
the pedestal cell. The pedestal cell is a type of
transfer cell and has tubular wall-ingrowths which
increases the surface area of its cell-surface membrane to accommodate more pumps. These
pumps are membrane-spanning proteins that pump chloride ions. (Chloride ions are negatively
charged and their charges attract and drag positively charged sodium ions with them). This
increases the salt concentration inside the cytoplasm of the pedestal cell, lowering its water
potential. Water then follows by osmosis (drawn out by the salt) as it moves from higher to lower
water potential. This water is replaced by water from the apoplast and a stream of water movement
through the apoplast is set-up. Water then moves from the pedestal cell into the basal cell and
surrounding tissues through the symplast (cell cytoplasms) moving from cell to cell through pores

The terminal cells possibly also secretes the enzymes to digest the prey when the trap is activated.
The products of digestion are absorbed by the terminal cells and are thought to follow the symplast
route (movement in the cytoplasm) moving from cell to cell through the plasmodesmata.

Once the trap has done its job, it is reset and can be used repeatedly. The water that is pumped
out every time the trap is reset has to be removed from the bladder and this is the function of the
external glands.
The external glands/trichomes consist of two cells - the pedestal cell and the terminal cell. Their
function is to excrete excess water taken up from inside the trap when it is reset. Water absorbed
by the external glands enters the tissues of the bladder wall and is transported from cell to cell
through the plasmodesmata until it reaches the external glands where it enters the pedestal cell
through plasmodesmata. The pedestal cell has tubular wall ingrowths (though not as extensive as
in the internal glands). These ingrowths increase the surface area of the cell-surface membrane
follows them passively by osmosis. The cuticle of the terminal cell is highly porous (especially when
stretched by water entering the terminal cell) and the water passes out through these pores.

The  relative lengths of and angles between the arms of the quadrifid glands are important
taxonomic characters in identifying species of
Utricularia (bladderwort)

Not all carnivorous plants use mechanisms as passive as those of pitcher plants. The next example we look at are
the aquatic bladderworts, or utricularias. These have extremely elaborate trap mechanisms!
Venus' Flytrap
Venus' Flytrap (Dionaea muscipula)

Similar to the bladderwort, the flytrap is a spring trap. Dionaea produces modified leaves as traps, with each trap
comprising a pair of valves. Each valve is fringed with hairs called cilia and has three trigger hairs, arranged in a
triangle, on its inside surface. Each plant produces 5-7 traps which are each 3-7 cm long.
Alluring glands inside the trap secrete a sugary mucilage to attract insects. When an insect touches one of the trigger
hairs electrical signals are generated. Initially these are local signals which decay rapidly over time and space. A
single brush does not activate the trap, otherwise many a false alarm such as a falling raindrop or debris could falsely
trigger the trap, but if any of the three hairs is touched again, then it generates a second electrical signal which is
added to the first. In this way, multiple touches that are close enough together in time will reach a threshold and the
trap will be activated. This process involves the transport of electrical signals throughout the plant neuroid/nervous
system (see the
sensitive plant).

When cells in the trap receive the signal, especially the hinge and central areas of the valves where most movement
occurs, then motor cells reversibly close the trap. The mechanism of closure is very different to the mechanism that
moves leaves to track the Sun - the pulvinus, or hinge joint at the base of a leaf stalk, has flexor and extensor cells
that swell and shrink reversibly as they take-up or lose water. In contrast, the movements that cause trap closure in
the flytrap are irreversible growth changes - flexor cells grow permanently larger. This growth appears to be triggered
by the active pumping of hydrogen ions out of the flexor cells and into the cell walls, lowering the pH of the apoplast.
This acidification of the cell walls activates wall-loosening enzymes, called
expansins, which break cross-links between
the cellulose microfibrils (microscopic fibres of cellulose) that make up the cell wall, allowing them to slide past
one-another and allowing the cell walls to stretch. As the cell walls looses, so the cells take in water and swell
irreversibly. Movement of water from the inner half to the outer half of the hinge provides the necessary water for the
flexor cells in the outer part of the hinge. This is a rapid example of the normal cellular growth process. Pumping of the
hydrogen ions is an energetic process and the cells use about 30% of their ATP (energy store) in this process.

Trap closure occurs in several stages:

1. Slow initial phase lasting 0.3s during which the trap only closes by 20%. During this phase, rapid growth of cells is
building up elastic energy which is stored inside the trap.
2. Rapid closure phase lasting 0.1s, during which time the trap closes by 60%. This is the phase that traps the
unfortunate insect before it has time to escape.
3. Second slow phase, during which the trap closes by the remaining 20% and lasting 0.3s.

Following closure is the appression phase, lasting about 30 minutes and during which the trap presses around its prey
and smoothers it in secreted mucilage. Following this is the sealing phase, during which the edges seal tightly to
prevent leakage of contents. This phase lasts for about one hour and is followed by enzyme secretion.

The cilia seal the edge of the trap after closure, but allow small prey to escape, since it is a waste of time the plant
digesting such small prey. If small prey escapes through the cilia, then the trap will soon open again (within 2 days).
Larger insects, however, cannot escape and the edges of the trap then more slowly form a tighter seal. Secreted
mucilage also entraps the insect and when the seal is formed, digestive enzymes are secreted and the prey liquefied
and absorbed. Digestion takes 4-14 days and the digestion glands give the inside of the trap its red colour (due to
anthocyanin pigment), which probably helps to attract insects. Extensor cells then grow larger and reopen the trap,
resetting it. Despite the fact that the growth changes are irreversible, successive growth cycles are possible and the
trap can be sprung and reset several times in its lifetime.

Venus Flytrap

Venus Flytrap

Above: note the triangle of sensory bristles on each valve of the trap.Usually there are 3 bristles per valve. The redness inside the trap is due to the production of anthocyanin pigment as a stress response to high light intensity. This does not harm the plant, however, the plant was originally very green when bought and still very healthy. Some varieties naturally produce more anthocyanins than others, even in lower light intensities.

Genlisea rhizophyll

Above: a rhizophyll of Genlisea, showing the vesicle (stomach) and the spiral arms with their slit-like openings. The
main mouth is in the junction of the two arms and hidden from view.

Genlisea - mouths, stomachs and all!

These small and remarkable rosetted herbs of South America and Africa have spatulate (spatula-shaped: having a
narrowed base and expanded tip) leaves lying on or close to the soil surface (epiterrestrial).
Genlisea has no roots,
but remarkably has modified root-like subterranean leaves, lacking in chlorophyll, called
rhizophylls, which form
subterranean traps for tiny soil organisms. The rhizophylls are tubular: the original adaxial (upper) surface of the leaf
forms the inside of the tube as the ancestral leaf has been rolled into a tube joined along the suture. Each rhizophyll is
constructed as follows: a short basal trap stalk (footstalk) widens into a hollow vesicle ('stomach') forming the digestion
chamber. This is followed by a narrow tubular neck which widens and forks into two branches (trap arms) which are
helically spiralled. The whole is roughly Y-shaped. In the region between the bases of the two branches is the main
mouth, though additional smaller slit-like mouths are arranged along the suture of the twisted trap-arms.

Bristles line the inside of the trap neck and arms and these are angled to point towards the stomach and presumably
serve to prevent prey from escaping. Multicellular glandular hairs line the vesicle and secrete the digestive fluids. Prey
includes mites, nematodes, protozoa, small algae, which are ingested along with soil particles and other debris. The
presence of soil particles and debris suggests that the traps are not passive and simply do not wait for organisms to
enter. Indeed, it has been shown experimentally that water-currents enter the traps, which presumably drag other
materials and organisms with them. The suction mechanism is not understood, but may be linked to transpiration
(detached rhizophylls lose their suction power - they need to be attached to the whole plant in order to work).

Some species have an additional elaboration: they exhibit trap dimorphism. They have larger and deeper traps and
smaller, more horizontal and shallower traps. These different trap types are presumably specialised to catch different
types of organism.

Semi-Carnivorous Plants

Many plants are not classed as fully-carnivorous but still 'eat' insects and make use of the nitrogen as a nitrogen
supplement. One such example of a semi-carnivorous plant is the

utricularia trap detail
Below: structure of a quadrifid or bifid gland, shown in section. (Based on the model of Fineran, 1985).
Above: e: external glands, i: internal glands: b: bifid, q: quadrifid; s: stalk; T:
trichomes; V: valve.
Above: Nepenthes (diagram based upon the type description and figures of Nepenthes
in Gronemeyer et al. 2014. Plants 3: 284-303). Species of Nepenthes are
extremely variable in pitcher form.
Nepenthes species use a variety of trapping mechanisms to catch prey. In some the peristome (the coloured rim
of the pitcher) is a wettable surface which easily becomes coated with a film of rain water or nectar, forming a
slippery surface. Insects alighting on the rim easily slip into the pitcher (wet capture). In others, the main
mechanism is the secretion of slippery wax crystals on the inside of the pitcher tube. These plate-like waxy crystals
easily detach, sticking to the adhesive pads of insect feet, contaminating them and making them more slippy dry
capture). Additionally, the wax seems to neutralise the sticky secretion of the insect's feet. Insect feet (tarsi) have
two primary adhesive mechanisms: tarsal claws and adhesive pads (see
insect locomotion). Both mechanisms
must be overcome for an insect to slip. Downward-pointing hairs (and the downward-pointing epidermal cells) on
the inside pitcher wall make it harder for the insect/arthropod to crawl back up and escape the trap.
has different varieties, with different pitcher forms, one relying on peristome capture, the other on a
slippery inner pitcher wall (10).

Nepenthes gracilis relies primarily on the lid, the undersurface of which secretes most of the nectar and is coated
in semi-slippery crystals of wax. An arthropod, such as an ant, stretching across the opening to reach the nectar
may be flicked into the trap by falling rain! Further, the digestive fluid of the trap may be highly viscous and sticky
and may contain alkaloids which anaesthetise the prey. (8)

Nepenthes aristolochioides has a pitcher with a translucent dome which acts as a light trap. Experiments have
shown that light transmitted through the pitcher dome is important in attracting and trapping small flies, such as
fruit flies (
Drosophila). (9)

Finally, many pitchers are detritivores rather than insectivorous, collecting and digesting falling plant debris.

Sarracenia Pitcher Plants (Trumpet pitchers)

Parrot Pitcher Plant

Above and below: Sarracenia psittacina, the Parrot Pitcherplant (Chelsea Physic Garden). The pitchers of this plant resemble those of Sarracenia minor except they are prostrate, forming a prostrate rosette whereas those of S. minor are erect. The hoods of S. psittacina also tend to form beak-like protuberances and look more parrot-like.

The traps of S. minor have hoods that hang down over the openings and translucent windows at the back. insects attracted to the nectar secreted by the trap rim and the edge of the wing (ala) which leads up to the rim, are attracted to the light passing through the windows so when they attempt to leave and fly away into the sky they aim for the windows instead and hit the back of the hood and slide down into the trap, which gets narrower towards the bottom, making it increasingly difficult for insects to reverse. Eventually they become trapped in the digestive fluid at the base of the pitcher.

Sarracenia psittacina has small openings and windows and backward-facing hairs make it hard for an insect that has entered the trap to escape. The prostrate traps are frequently submerged by water and catch arthropods and tadpoles and works more like a 'lobster pot' trap whereas the upright pitchers of Sarracenia minor operate as pitfall traps. The Parrot Pitcherplant sometimes also produces semi-erect pitchers with reduced wings (alae).

Parrot Pitcher Plant

There are 8 to 11 recognised species of Sarracenia and these plants span the subtropical, temperate and Arctic zones of North America. Most occur in the USA, but the Northern Pitcherplant, Sarracenia purpurea, extends into Canada. Sarracenia minor is much more southern and grows in bogs in openings in pine forests in North Carolina, South Carolina, Georgia and Florida (regions that are chiefly subtropical). (External link: Botanical Society of America).A giant form of S. minor, the Okefenokee Giant variety, var. okefenokeensis also occurs. Sarracenia psittacina occurs from Georgia to Louisiana again in subtropical pine forests. Similarly, a gigantic form of S. psittacina, var. okefenokeensis has pitchers reaching over 30 cm in length.

The plant below was purchased from Chelsea Physic Garden, London (without reading the labels carefully). It is clearly a hybrid and after careful consideration I have decided that is most probably Sarracenia x Swaniana. Sarracenias hybridise easily and hybrids may consist of 2 or more parent species in differing proportions. The hybrid Swaniana is a cross between Sarracenia purpurea and S. minor (Sarracenia purpurea x S. minor).

Sarracenia X Swaniana Pitcher Plant

Note the drops of nectar on the edge of the ala and the rim of the trap and the tracts of downward-pointing hairs on the inside of the hood. The shape of the hood and the tracts of hairs are very suggestive of Sarracenia purpurea as is the wavy ala. Note also the translucent windows, suggestive of S. minor. (The transparent trays were eventually replaced with opaque ones since they encouraged the growth of cyanobacteria and it was not sure what effect nitrogen fixation and secretion of other materials by these organisms into the water would have on the pitcherplant, although there are lower numbers of cyanobacteria in the surface soil of course).

Sarracenia X Swaniana Pitcher Plant

The pitchers slowly reddened at their top ends whilst sitting on the windowsill, beginning with the veins. This red coloration is due to the pigment anthocyanin. The amount of anthocyanin produced depends on the species and variety and also on exposure to light and perhaps heat. The anthocyanins are produced when the plant is stressed by excessive radiation and help to protect the chlorophyll against bleaching. This does not necessarily mean that a red plant is unhealthy since plants that often grow in the open must shield themselves from UV light and in some plants, those anticipating very bright sunlit conditions, anthocyanin synthesis is often constitutively switched on so these plants always tend to be reddish. By the same token, reddness is not necessarily an indication that the plant is getting 'enough' light since this plant was mostly green when purchased but evidently very healthy.

This plant is growing near to open windows in the summer and so has caught some of its own food, though this has been supplemented by rehydrated mealworm pieces. the large tray is constantly filled with deionised water to about an inch in depth. This generates a moist enough atmosphere to prevent the tops of the pitchers from drying out (a problem that occurred early on and was quickly remedied). Not all deionised waters appear to be suitable, however, and when a good supply of water is found I think it's advisable to stick with it. Although this water has neutral pH, it has been claimed that the plants may prefer slightly acidic water as would be found in their natural bog/fen/seepage marsh habitats. this particular hybrid appears to grow well indoors and once the conditions are right then it will grow vigorously, but if anything is not quite right then the pitchers and roots will quickly begin to die back. Sarracenias do have particular requirements but grow vigorously once conditions are suitable.

Sarracenia X Swaniana Pitcher Plant

Note that the developing leaves are mostly blade (ala) with no traps to begin with no trap, then the trap cavity develops and eventually the trap opens and the hood expands. The smaller traps are not developing traps but mature small traps and are a deliberate part of the plant's growth strategy. However, larger traps generally catch more prey, though studies in Sarracenia pitchers have shown that in nature as many as 50% of pitchers may fail to catch anything. The newer pitchers began to produce copious nectar, which may reflect the ample light for photosynthesis or the age of the traps or perhaps the plant was not catching enough insects. The large frilly openings in the larger pitchers is a character inherited from S. purpurea. Some of the smaller traps appear more covered as are the traps in S. minor.

Sarracenia purpurea forms large sac-like traps with large opening that are not covered. These traps will catch falling debris in addition to insects and other small invertebrates and micro-organisms. There is some controversy over whether or not this species produces digestive enzymes or relies on digestion carried out by the microbial and invertebrate communities that accumulate in the open traps and simply absorb what is produced by them. However, research has clearly shown that although individual traps may persist for two years in this species, they catch most of their prey within the first 50 days after opening. Within the first two weeks liquid within the traps contained digestive enzymes (proteases, nucleases and phosphatases) even though the microbial count was very low. This suggests that traps of Sarracenia purpurea do indeed synthesise some of their own enzymes, especially early on. Although this enzyme secretion switched off later on, the necessary genes would switch back on if arthropods (or raw nutrients) were introduced into the traps. However, older traps do indeed have communities of microbes and support the development of the larvae of specialised species of insect, such as the Mosquito Wyeomyia smithii and the moth Endothenia daekeana. They also house the copepod Paracyclops canadensis (which is rare elsewhere). These organisms grow and develop inside the liquid of the pitchers without being digested, suggesting that older traps either eventually lose their ability to produce digestive enzymes or that the inhabitants send some signal to switch them off or that the enzymes are fended off by living organisms, e.g. by lipid or mucus secretion. Parts of plants that trap water that may house unique ecosystems are called phytotelmata (sing. phytotelma).

Sarracenia X Swaniana Pitcher Plant

The leaf form on individual Sarracenia plants is subject to environmental regulation. Some of the leaves produced are phyllodia (not to be confused with phyllode) in which the keel (wing or ala) becomes the prominent feature of the leaf with the trap itself reduced or absent. There is a continuous spectrum from leaves which are predominantly traps to leaves which are predominantly phyllodiae. Experiments in Sarracenia purpurea have shown (12) that supplying the plants with more nitrogen increases the proportion of leaves which are phyllodiae. This makes sense: the leaves are important organs of photosynthesis and producing traps is expensive so when nitrogen is plentiful leaves develop into phyllodiae.It should be noted that the juvenile leaves of Sarracenia begin as phyllodiae with the traps expanding and opening as the leaf matures, which suggests that when nitrogen is plentiful some of the genes for leaf maturation are switched off, leaving the leaves to continue growth with juvenile characters. Of course the leaf evolved before the pitcher and the developing leaf repeats this trend, to some extent, as it grows and so begins much as a normal leaf with the trap developing and opening later.

Sarracenias are perennials, overwintering largely as an underground rhizome, though the leaves in Sarracenia purpurea are evergreen and last for over a year. In most species the pitchers die back over winter. The amount of short days and cold nights that a pitcherplant needs to induce its overwintering dormant state obviously depends on the species and its natural latitude. The Swaniana hybrid here has one parent from the subtropics and one from the arctic, so it will be interesting to see how it manages. Sarracenia purpurea and S. flava have been planted out in several wild locations in Britain and are apparently doing well.

Sarracenia X Swaniana Pitcher Plant

The flower of Sarracenia hangs upside-down on a long pedicel. There are three bracts, five sepals and five petals. the style expands out into an umbrella which traps pollen that falls from the numerous stamens. Insects entering the flower, perhaps seeking refuge, may pick up some of this pollen. The umbrella is pentamerous (with fivefold radial symmetry) and bears stomata and is photosynthetic and bears five radial veins. Near the tip of each vein is a small projection inside the umbrella which is the stigmatic surface. The petals are arranged such that insects can only enter the flower by passing past a stigma and they may deposit any pollen they are carrying here. The five veins contain pollen-tube conducting tissue as well as vascular tissue. the conducting tissue forms a hollow tube for the pollen tube to grow through, guiding it to the ovules inside the ovary, a distance of about 4 cm. On this long journey the umbrella must nourish the growing pollen tube, which is presumably assisted by the fact it carries out its own photosynthesis (14).

Sarracenia flower diagram

Sarracenia flower diagram

Sarracenia flower diagram


  1. Glandular trichomes in Utricularia: a review of their structure and function. Fineran, 1985.
  2. Kinetics and Mechanism of Dionaea muscipula Trap Closing. Volkov et al., 2008. Plant Physiology
    146: 694-702.
  3. Leaf Closure in the Venus Flytrap: An Acid Growth Response. Williams and Bennett, 1982. Science
    218: 1120-1122.
  4. A quantitative study of tissue dynamics during closure in the traps of Venus's flytrap Dionaea
    muscipula Ellis. Fagerberg and Allain, 1991. Am. J. Bot. 78: 647-57.
  5. http://ejournal.sinica.edu.tw/bbas/content/2011/1/Bot521-06/Bot521-06.html
  6. http://www.bsbi.org.uk/Utricularia_Crib.pdf
  7. Four New Species of Nepenthes L. (Nepenthaceae) from the Central Mountains of Mindanao, Philippines, 2014.
    Gronemeyer, T., F. Coritico, A. Wistuba, D. Marwinski, T. Gieray, M. Micheler, F. S. Mey and V. Amoroso. Plants
    3: 284-303.
  8. With a Flick of the Lid: A Novel Trapping Mechanism in Nepenthes gracilis Pitcher Plants, 2012. U. Bauer, B. Di
    Giusto, J. Skepper, T. U. Grafe, W. Federle. PLoS ONE 7: 1-7.
  9. The use of light in prey capture by the tropical pitcher plant Nepenthes aristolochioides, 2012. J. A. Moran, C.
    Clarke and B. E. Gowen. Plant Signaling and Behaviour 7: 957-960.
  10. Evidence for alternative trapping strategies in two forms of the pitcher plant, Nepenthes rafflesiana, 2011. U.
    Bauer, T. U. Grafe and W. Federle. Journal of Experimental Botany, 62: 3683–3692.
  11. Phylogenetic relationships, systematics, and biology of carnivorous Lamiales, with special focus on the genus
    Genlisea (Lentibulariaceae), 2011. A. Fleischmann.
  12. Nitrogen availability alters the expression of carnivory in the northern pitcher plant, Sarracenia purpurea. Ellison, A.M. and Gotelli, N.J. 2002. PNAS 99(7): 4409-4412.
  13. External link: http://www.carnivplants.org/index.html
  14. The development and anatomy of Sarracenia purpurea: contributions from the botanical laboratory of the Johns Hopkins University no. 5. Shreeve, F. 1906. Botanical Gazette 42: 107-126.

Article last updated:
17 March 2015
17 Dec 2015
22 Sep 2019